In semiconductor manufacture, a single semiconductor die is typically mounted within a sealed package. Semiconductor packages (or chips) come in a variety of different designs. Among the different package designs are dual inline packages DIP, zig-zag inline packages ZIP, small outline J-bends SOJ, thin small outline packages TSOP, plastic leaded chip carriers PLCC, small outline integrated circuit SOIC, plastic quad flat pack PQFP, and interdigitated leadframe IDF.
In general, all package designs incorporate several common elements. These common elements include a sealed package enclosure, a die-attachment area, bonding wires for making electrical contact between the bond pads on the die and the leads of the package, and the inner and outer lead fingers of the metal lead system for the package.
Typically, the initial component in the packaging process is a leadframe or leadframe strip. A leadframe strip is a metal frame which is several inches long. The leadframe strip supports each semiconductor die for packaging and provides the leads for the final semiconductor package. A typical leadframe strip is produced from metal sheet stock (e.g. a copper alloy) and is adapted to mount several (e.g. eight) semiconductor packages. During the manufacturing process each leadframe strip is moved and indexed through the various manufacturing stages as a unit.
In a conventional semiconductor packaging process, the dice are initially attached to mounting paddles of a leadframe strip. During a wire bonding process, the bond pads formed on the face of each die are connected to the lead fingers of the leadframe strip using fine bond wires. The semiconductor dice are then encapsulated and a trim and form operation is used to separate the resultant interconnected packages and to bend the leads of each semiconductor package into the proper configuration.
The present invention is directed to the wire bonding process. Apparatus for wire bonding semiconductor dice are well known in the art. U.S. Pat. No. 3,894,671 to Kulicke Jr. et al, U.S. Pat. No. 4,877,173 to Fujimoro et al, and U.S. Pat. No. 5,082,165 to Ishizuka, disclose representative wire bonding apparatus. Earlier versions of wire bonding apparatus were manually operated by an operator viewing the semiconductor die through a microscope. More recently, automated wire bonding apparatus include vision systems for automatically sensing the locations of the bond pads on the dice and lead fingers of the leadframe to perform the wire bonding process.
During the wire bonding process a single die attached to a leadframe is held between a wire bonding clamp and a wire bonding heat block of the wire bonding apparatus. The heat block heats the semiconductor die and the leadframe to a temperature of about 150.degree. C. to 350.degree. C. A bonding tool then mechanically presses a fine bond wire to a bond pad of the die and then to a bonding site on an appropriate lead finger.
The bond wire is typically a fine gold or copper wire that is threaded through the bonding tool. The end of the wire is heated by an electrical discharge or a hydrogen torch to a molten state. This forms a ball of molten metal on the end of the bond wire. For bonding a selected bond pad of the heated die, the molten ball is pressed by the bonding tool against the bond pad. This mechanically bonds the bond pad and bond wire to one another. The bonding tool is then moved over a bonding site on the lead finger and the heated bond wire is pressed against the bond site. This mechanically bonds the bond wire and the lead finger to one another. The bond wire is then tensioned and sheared. This process is repeated for each bond pad on the die.
A critical step of the wire bonding operation is the initial indexing of a leadframe strip. Prior to the wire bonding step, an indexing assembly of the wire bond apparatus precisely moves the leadframe strips to place the dice one at a time between the wire bonding clamp and the wire bonding heat block. This indexing step must be performed for each die on a leadframe. Misplacement of the leadfree or die during the wire bonding process may cause the wire bond apparatus to jam and the wire bonds to be misplaced. Moreover, an indexing step for each die on a leadframe is relatively time consuming and adds to the complexity of the wire bonding process. The present invention recognizes that the wire bonding process can be simplified and improved if two or more dice are wire bonded with a single index of a leadframe strip. At the same time, the speed and throughput of the wire bonding process can be improved.
Accordingly it is an object of the present invention to provide a method and apparatus for wire bonding bond pads on semiconductor dice to the leadfingers of a semiconductor leadframe. It is a further object of the present invention to provide a method and apparatus for wire bonding multiple semiconductor dice on a leadframe with a single indexing strip of the leadframe. It is yet another object of the present invention to provide a method and apparatus for wire bonding bond pads on a semiconductor die to the lead fingers of a leadframe that is fast, efficient and adaptable to large scale semiconductor manufacture.